It has been known in the art for some years that when the modern dairy cow transitions from a non-lactating state to a lactating state during the periparturient period, she undergoes tremendous physiological challenges resulting in an overall state of immune suppression. These changes are characterized by inflammatory conditions, susceptibility to metabolic disorders, uterine and mammary infections, and loss of appetite. These stresses are further complicated by the fact that the sudden initiation of an increase in milk production means that the animal is metabolically in a state of negative energy balance during the immediate postpartum period (approximately eight to ten weeks).
Many of the stress symptoms that individual cows experience go unnoticed. Not only are the animals' health and welfare compromised, but there are also significant economic implications. These animals will have difficulty conceiving, thereby exacerbating losses. To have reliable biomarkers of inflammatory and health status that can be routinely measured is of critical importance to detect, intervene, and manage at-risk cows as early as possible. Subclinical ketosis (SCK) is defined as elevated concentrations of circulating ketone bodies in the absence of clinical signs.
SCK has been found to be associated with high risk of clinical ketosis and displaced abomasum. In addition, subclinically affected cows appear to have reduced milk production than those with normal ketone body concentrations. The economic losses caused by SCK may be huge due to the treatment costs, decreased milk yield and decreased reproductive efficiency. An estimated 40 to 60 percent of cows in North America dairy herds are affected by early lactational incidence of SCK, which is much higher than the two to fifteen percent incidence with clinical ketosis.
Determination of β-hydroxybutyrate (BHBA) is considered as the golden standard to diagnose subclinical ketosis. Cows with BHBA in their blood, milk, and urine typically experience a period of negative energy balance. The detection of ketosis clinical signs varies, but blood BHBA concentration of 1.2˜2.9 has been used as the upper threshold for SCK.
Early detection of SCK by measurement of BHBA concentration will help farmers, as these diseases generally have a poor prognosis for production and survival. BHBA in cows' blood and milk are commonly used to diagnose SCK. Monitoring blood BHBA is superior to monitoring urine due to its stability. At present, such tests may be determined spectro-photometrically by traditional clinical laboratory means, and would require the producer to send samples to a lab and wait for the results, a process which is inconvenient and expensive. The advantage of detecting blood BHBA is that no rigorous sample handling precautions are required during the specimen transportation due to the reasonable stability of BHBA in blood.
One obvious advantage of using milk instead of blood for analysis of ketosis is the noninvasive nature of milk sampling. However, because of its nontransparent nature, opacity of the sample is incompatible with spectrophotometry. Consequently, milk needs extensive pretreatment when using traditional analytical methods, typically, precipitation, centrifugation, and special harvesting are necessary. Current cow-side milk testing techniques for BHBA are not accurate and only semi-quantitative results are obtained.
What is needed is a reliable method of SCK detection that can be conducted on-site using serum samples or milk samples.